1. Field of the Invention
The present invention is directed to liquid crystal display panels. More particularly, methods and systems relating to supporting blending functionality (e.g., “picture in picture” display, hereinafter “PiP”) and overdrive functionality in a versatile display pipeline architecture are provided.
2. Discussion of the Related Art
Liquid crystal display (LCD) panels are used in a wide range of electronic products, including computers, monitors, flat panel displays, and televisions, among others. LCD displays are matrices of liquid-filled cells that form pixels. When voltage is applied to a pixel, the pixel becomes transparent to light, the transparency increasing with voltage. Thus, by varying the amount of voltage applied to the pixel, different luminance levels can be achieved. LCD panels offer the high resolution, refresh rates, and response times necessary for high-definition viewing of software, graphics, videos, and other media. LCD panels are typically controlled by a display system controller, such as the SupraHD® 780 processor from Zoran Corporation of Sunnyvale, Calif.
LCD panels are essentially a type of “sample and hold” device. As such, they are known to suffer from motion blur and other undesirable artifacts that are a result of the time lag that occurs between the moment a voltage is applied to a pixel and the moment when the pixel achieves the steady-state luminance for that voltage. Therefore, in many systems incorporating LCD panels, overdrive functionality is used to reduce motion blur and other artifacts resulting from this time lag. In these systems, image data for both a current frame and an immediately prior frame is provided to an overdrive processing unit. The overdrive processing unit determines from the current data frame what the luminance value should be for each pixel as well as the corresponding voltage required to generate that level of luminance. The overdrive processing unit also accesses the immediately prior data frame to determine an adjustment in voltage that can be made from the immediately immediately prior data frame to achieve the proper luminance for the current data frame. The overdrive processing unit may calculate this value on its own or it may refer to a lookup table where, for each pair of voltages corresponding to the immediately previous voltage and the current voltage of a given pixel, a target voltage is provided. This target voltage is used to generate the luminance for the pixel for the current frame.
The general concepts associated with using overdrive to reduce or eliminate undesirable artifacts when driving an LCD panel are illustrated in FIG. 1. As can be seen, there is a time lag between the moment a voltage V2 is applied to a pixel of an LCD panel cell at luminance level L1 and the moment at which the luminance level L2 is achieved, where the luminance level L2 is the steady state luminance that would be achieved by applying voltage V2 to the pixel for a prolonged period of time (i.e., over several frames). This time lag may have a duration 110 in the range of 33 ms, for example, whereas each frame of video data (e.g., frame Fn−1, frame Fn frame Fn+1, frame Fn+2, etc.) only has a duration 120 of 16 ms long.
Referring still to FIG. 1, by applying to the pixel a voltage V2′ that is higher than the voltage V2 that will maintain the pixel at luminance L2, the pixel is “overdriven” and achieves desired luminance L2 in a much shorter duration 130, for example, 12 ms. Since the desired luminance L2 is achieved during the current frame Fn (rather than two frames later, in the case where voltage V2 is applied), motion blur and other artifacts can be reduced or eliminated along with the aforementioned time lag.
Methods are known in the art to modify the pixel data for a given video data frame to take advantage of this overdrive effect. For example, with reference again to FIG. 1, a pixel in the current data frame has a desired luminance value of L2, whereas the same pixel in the immediately prior data frame had a luminance value of L1. The pixel in the current data frame can be modified to have a luminance value of L2′, which causes the display device, when it displays the pixel, to apply voltage V2′ to the pixel and thereby achieve the overdrive effect described above.
Another illustration of modifying pixels to take advantage of the overdrive effect is shown in FIG. 2, using exemplary luminance values. In frame N, a target luminance value of 150 is desired. However, the same pixel in the immediately prior frame N−1 had a luminance value of 100. To overcome the time lag associated with modifying the luminance from 100 to 150 during the current frame, the pixel in the current frame may be modified to have a luminance value of 175. This causes a correspondingly higher voltage to be applied during the current frame, which in turn causes the pixel to more quickly achieve an actual luminance value of 150 so that it is achieved during the current frame. Similarly, in the following frame N+1, to achieve a target luminance value of 100, the pixel may be modified to have a luminance value of 75 to more quickly decrease from a luminance value of 175 to 100 during the current frame.
It will be appreciated that the term “overdrive” as used herein refers to modifying the to luminance value of a pixel to be either higher or lower than the target luminance value depending on which direction the luminance is being modified. In other words, “overdrive” refers to both “overshooting” and “undershooting” the target luminance value of a pixel.
LCD panels incorporating overdrive functionality in the past have required an overdrive memory buffer for storing the immediately prior frame of data, such that the luminance values therein can be referenced in carrying out the overdrive techniques discussed above. This memory buffer increases the size, cost, and complexity of the LCD panel system.
Blending is a technique used in display devices to allow two different data sources (for example, two different channels on television) to be displayed simultaneously. One common example of blending is the “picture in picture” (“PiP”) feature seen on some televisions. In PiP mode, a first data source may be displayed on a television. However, a portion of each frame of the first data source may be removed and replaced (i.e., blended) with a reduced-size version of a current frame of the second data source. This “picture within a picture” can be displayed in a corner of the larger display, and its size and position may be configurable as well.
Blending may also be used to achieve a “side by side” (“SBS”) feature. In SBS mode, each frame of data from two data sources may be reduced in size and displayed in distinct areas of the display device, either side-by-side or in any other desired orientation.